Art of submarine signaling.



W. HAHNEMANN 8: H. HEGHT.

ART OF SUBMARINE SIGNALING.

APPLICATION FILED MAY 22, 1913.

1,1 33,635. Patented Mar. 30, 1915.

marrnp STATES PATENT oFFioE.

WALTER HAHNEMANN AND HEINRICH HEGHT, KIEL, GERMANY.

ART OF SUBMARINE SIGNALING.

To all whom it may concern Be it known that we, WALTER HAHNE" MANN, engineer,'a subject of the German Emperor, residing at 214 Holtenauerstrasse, Kiel, Germany, and Dr. HEINRICH Hr on'r, a subject of the German Emperor, residing at 62 Holtenauerstrasse, Kiel, Germany, have invented certain new and useful Improvements in the Art of Submarine Signaling; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertams to make and use the same.

The present invention relates to the art of receiving submarine sound signals, wherein there is employed a receiving system or systems of sensitive characteristics capable of detecting sound waves throughout a suitable range of periodicity and of the amplitude remaining to the sound waves after hein propagated through the sea from a conshferable distance. In most systems of this kind, a microphone in the form of a telephone transmitter is used in c0n]unct1 on with a telephone receiver to'render the signals apparent to an observer. In apply ng such systems to ships, the difficulty exists that there is available no abutment which will remain stationary as the hull vibrates for fixing one electrode of the microphone. It has been attempted to overcome this difficulty by connecting to the ships hull a socalled inertia microphone in which, upon vibration of the ships hull due to the sound waves received from the water, a mass of carbon powder or the like is shaken between the two relatively fixed electrodes of the microphone to thereby change the resistance of the microphone and produce a signal in the telephone receiver. However, a shaklng microphone has, proven to be insufliciently sensitive to the sound waves received from the sea, which are of exceedingly small amplitude. Resort has been had the interposition of an element of definite individual period of vibration, such as a resilient ring or the like, between the ships hull and the microphone, the receiving system being tuned to the periodicity of the sound waves. In this way, it is also possible to use a pressure microphone which is located between two points of the transmitting ele- Speciflcation of Letters Patent.

Patented Mar. 30, 1915.

ment having a different phase of vibration, or a different amplitude of vibration, whereby the microphone is subjected to pressure sufficient to produce a signal in the telephone receiver. This arrangement gives better results, but by merely tuning the oscillatable system which is located between the ships hull and the pressure microphone serving as the receiving device, only a small portion of /the received energy can be made effective on the microphone to render the signals apparent in the telephone receiver.

In accordance with this invention, the receiving system, in contrast to mere attuning, is so constructed and arranged that the damping of the oscillations of the intermediate member by the hull wall is substantially equal in amount to the damping of that member by the microphone receiver. The system com rises the intermediate element having a efinite period of vibration and attached to a' structural part, (such, for example, as a skin plate of the hull) re sponsive to sound waves propagated through the sea, and carrying a pressure microphone mounted between points of the intermediate member having different phase or different amplitude of vibration so as to be subjected to pressure variations upon vibration of the intermediate member, together with 'the usual adjuncts for rendering the resistance variations apparent as signals. In the preferred form of apparatus for this purpose, the transmitting element is a tuning fork attached its stem to the inside of the skin of the ship, and the pressure microphone is mounted between the prongs of the tuning fork, a telephone receiver together with the necessary battery or the like being used to receive the signals. In such a system the amplitude of the vibrations of the tuning fork is damped on theone hand by the vibrations radiated from the receiving device back to the sea, this effect being termed herein radiation damping effect, and on the other hand by the vibrations of the electrodes of the pressure microphone, this effect bein termed herein useful damping effeet and it has been found that the maxi-v mum eifcct is produced on the microphone. receiver or the like when the amount of the radiation damping effect is substantially equal to the amount of the useful damping effect. However, it has been found in practical operation that a receiving system thus brought to the condition of maximum sensitiveness is not only exceedingly sensitive to the sound waves desired to be received, but also to other disturbing vibrations. Moreover, it has been found that the sensitiveness o fthe receiving system to disturbing vibrations diminishes rapidly as the amount of radiation damping effect is made less than that of the useful damping efiect, while at the same time the sensitiveness for sound waves, which usually correspond to high periodicities, is not diminished at the same rate. Therefore, ifthe maximum sensitiveness of the receiving system is desired, especially when sound signals are received in still water, the radiation damping effect should be made substantially equal to the useful damping effect, but if moderate sensitiveness without disturbin efiects is desired, the radiation damping e ect should be diminished. Also, if'a comparatively wide range of sensitiveness is desired, two or more receiving systems of this kind should be used,

one being adjusted to have substantially equal radiation and useful damping effects, and the other or others being adjusted to have a relatively less radiating damping effect, the two or more receiving systems then being used selectively if desired.

In the foregoing discussion it has been assumed that the tuning fork is tuned as nearly as possible to the periodicity of the sound waves received. However, in practical .oporation": in which bells usually form the source of the sound waves to be received, it has been. found that the bells are not exactly tuned and also have their itch varied by temperature and other in uences. In such cases, the range of sounds to which the accurately tuned fork is sufficiently sensitive is quite narrow, so that although the previously described receiving system is well adapted for overcoming the disturbing infl uences, its range is not sufficient for practical requirements in which the periodicity of the sound waves varies. It has been found that this latter difficulty can benicely met by tuning the two prongs of the tuning fork to different periods of vibration, the preferred arrangement being such that the two periodicities attained cover approximately the range to which the pitch of the bell varies in practical operation. This expedient reducesthe sensitiven'ess of the receiving system compared with that of a re cciving system accurately tuned to the pitch of the bell, but the range over which the receiving system is sufficiently S6I1Sltl"6 is considerably increased. Instead of providing differently tuned prongs to the tuning fork, it is possible to utilize a plurality of differently attuned receiving systems, the

' telephone. receiver or the like being connected to the pressure microphones selecing fork is less damped than a smaller one,

other conditions bein the same. Also, the radiation damping e ect is varied by altering the point of attachment of a tuning fork to a ship or other structure responsive to the sound waves propagated by the sea, the

effect being reduced to a minimum when the stem of the tuning fork is so'attached, and

the efiect being increased to the maximum when the end of a prong of the tuning fork is so attached.- However, the preferred method of varying the radiation damping effect is to interpose a yielding connection between the tuning fork and the hull of the ship or other structure. If. a spring is used for this purpose, it can be arranged so as to have a variable initial tension, or the relative position of the pointsof attachment of the spring to the ship or other structure and to the tuning fork can be varied. In general, the radiation damping effect is remore and more yielding. The useful damp.- ing effect of the microphone varies with the relative size of the microphone and the tuning fork, but this method is applicable over of the microphone is greater than desiredwhen the microphone is mounted between .the ends of the prongs of the tuning fork,

and then adjusting the useful damping effect to'the proper relative value by moving the duced in this way as the connection is made points of connection of the microphone toward the stem of the tuning fork. The two prongs of the tuning fork may be tuned to different periods of vibration by attaching an adjustable weight to one of the prongs and shifting it along the prong until the best position is found. The desired effect may be secured in other, ways, such as by making or filing one prong thinner than the other.

The accompanying drawing illustrates diagrammatically a preferred embodiment of our invention having a series of receivers individually adapted to differentspecific purposes.

In the drawing, the stem of the tuning fork B is screwed into the hull A of the ship, or the like, and the pressure microphone C is adjustably mounted between the prong near theouter ends thereof so as to be responsive to vibrations of the tuning fork set up by the waves propagated through the sea to the hull A from any source of sound signals (not shown). The tuning fork B is attached to the hull A through the intermediacy of an adjustable spring S, and the microphone C is adjustably mounted between it s prongs as shown. Each of the tuning forks has, or may have, a sliding weight WV fastened to one of its prongs so as to give that prong a different period of vibration than the other prong of the tuning fork. The telephone receiver E is installed at any convenient point on the ship, and is electrically connected on one side to the battery D which is also connected to one terminal of each microphone C and C. The other terminal of the telephone receiver, is electrically connected to the central terminal of a two-way switch T, the other terminals of which are individually connected to the other terminals of the -microphones, as shown.

The tuning fork B and microphone C are adjusted for maximum sensitiveness by making the radiation damping effect substantially equal to the useful damping effect, the microphone being adjusted to that point along the prongs at which this result is attained. Thus, this receiving system is made exceedingly sensitive to sound waves of its period of vibration, but, as has heretofore been explained, it is also sensitive to interfering disturbances, the result being suitable for receiving sound waves in still water. The tuning fork B and the microphone C constitute a receiving system in which the radiation damping effect is made less than the useful damping effect by means of the adjustable spring connection S between the stem of the tuning fork and the hull A. Thus, this receiving system is suitable for sound waves of its period and although it is less sensitive to the sound waves which are desired to be received, it is also less sensitive to interfering disturbances. Either or both tuning forks may have its two prongs adjusted to different periods of vibration by means of the sliding weight W, so that its microphone will respond to sound waves over a wider ran e of periodicity. By connecting the telep one receiver E to the two microphones C, C in turn by means of the switch T, the most suitable receiving system is obtained under any condition.

It will be apparent that more or less than the two tuning forks with their associated pressure microphones may be used, and that the same or different equipments may be installed on the other side of the ship as well, in order to cover a wider or difi'erent range of conditions. Furthermore, if desired, a separate telephone receiver may be used for each microphone, so that the switch T would then be eliminated.

Having thus described our invention, what we claim is 1. In apparatus for receiving submarine signals, a tuning fork adapted for attachment to a structural part which is responsive to sound waves propagated through the sea, a pressure microphone cooperative with the tuning fork so as to be subjected to pressure upon vibration thereof, and means responsive to the microphone for rendering said vibrations apparent; substantially as described. i

2. In apparatus for receiving submarine signals, a tuning fork adapted for attachment to a structural part which is responsive to sound waves propagated through the sea, and having differently tuned prongs, a pressure .microphone cooperative with the differently tuned prongs of the tuning fork so as to be subjected to pressure upon vibration thereof, and means responsive to the microphone for rendering said vibrations apparent; substantially as described.

3. In apparatus for receiving submarine signals, a tuning fork adapted for attachment to a structural part which is responsive to sound Waves propagated through the sea, a 7 pressure microphone adjustably mounted between the prongs of the tuning fork so as to vary the useful damping effect relatively to the radiation damping effect of the receiving system, and means responsive to the microphone for rendering apparent the vibration impressed upon the microphone; substantially as described.

4. In apparatus for receiving submarine signals, a tuning fork adapted for attachment to a structural part which is responsive to sound waves propagated through the sea, a pressure microphone mounted between the prongs of the tuning fork so as to be subjected to pressure upon vibration thereof, and means responsive to the microphone for rendering said vibrations apparent, the amplitude of vibration of said tuning fork and the amplitude of vibration of said microphone being so adjusted that the radiation damping effect is less than the useful damping efi'ect, whereby the sensitiveness of the receiving apparatus is reduced to thereby reduce the efiect of interfering vibrations; substantially as described.

5. In apparatus for receiving submarine signals, a yielding support attached to a structural part which is responsive to sound waves propagated through the sea, an element having a definite period of vibration and attached to the yielding support, a pressure microphone cooperative with the'said element so as to be subjected to pressure upon vibration thereof, and means responsive to the microphone for rendering said vibrations apparent, the amplitude of vibration of said element and the amplitude of vibration of said microphone being so adjusted that the radiation damping effect does not exceed the useful damping effect; substantially as described.

6. In apparatus for receiving submarine signals, a yielding support attached to a said vibrations apparent; substantially as 10 structural part which is responsive to sound described. waves propagated through the sea, an ele- In testimony whereof we afiix our signament having a definite period of vibration tures, in presence of two Witnesses.

5 and attached to the yielding support, a VYALTER HAHNEMANN.

pressure microphone cooperative wlth the D-RQHEINRICH HECHT. said element so as to be subjected to pres- Witnesses: sure upon vibration thereof, and means re- KARL FRIEDRICH FRENTEL,

sponsive to. the microphone for rendering FRANs KUMMEL. 

